The objectives of this project are three-fold. First we plan to develop a screening test for suspected renovascular hypertension more sensitive and specific than the rapid sequence intravenous pyelogram. Secondly we hope to improve on the value of bilateral renal vein renin data as a prognostic indicator of surgical cure of hypertension in hypertensive patients with known unilateral or bilateral renal artery stenosis. Lastly we hope that our test will be useful in monitoring renal blood flow in patients over the short and long term following renovascular surgery. To accomplish these aims we will develop a quantitative technique to measure relative and absolute renal blood flow between the kidneys without ureteral catheterization. The technique will be quick, inexpensive and non-invasive. The estimate of relative renal blood flow will use first-pass external counting data over the abdominal aorta and kidneys following peripheral intravenous injection of 99mTc-albumin. The data will be obtained by a scintillation camera interfaced to a small digital computer. The analysis of the data to obtain relative renal blood flow is based on fundamental principles of dye-dilution theory. The core of the analysis involves fitting the gamma variate function to the aortic and kidney external counting curves from which the mean transit time of 99mTc-albumin through each kidney is derived. The estimate of relative renal blood flow will be converted to absolute renal blood flow by obtaining the plasma clearance of 131 I-hippurate following peripheral injection. This latter technique has been automated for small computers and requires only two blood samples along with external counting data over the precordium or head. The entire analytic technique for measuring both relative and absolute renal blood flow will be almost completely automated on the small computer interfaced to the scintilation camera such that only a minimum of operator interaction will be required.